This invention relates to apparatus for providing a high bit rate or wideband switched transmission paths for a digital switching system that has fixed a bandwidth switched transmission paths. The apparatus is used to increase the bandwidth available to an individual user. The embodiment described herein is implemented in a distributed control switching system but the apparatus and concepts are applicable to any centralized switching system of the type capable of establishing independent switched paths of a fixed bandwidth. Thus while a distributed control system is described, the technique is applicable to any digital switching system with independent switched path set-up.
Essentially, a distributed control communication system has evolved providing a novel switching network architecture. In this architecture, there is no separately identifiable control or centralized computer complex, since the control for the switching network is distributed in the form of multiple processors throughout the subsystems, with such distributed processors providing the necessary processing functions for the subsystems serviced.
Thus groups of control functions for certain systems are performed by processors dedicated to those subsystems; however, other processing functions of the same subsystems which may be more efficiently performed by other processors are performed by such other processors. An example of such a system can be had by referring to U.S. Pat. No. 4,201,890 entitled MULTI-PORT DIGITAL SWITCHING ELEMENT, issued on May 6, 1980 to A. J. Lawrence et al and assigned to International Telephone and Telegraph Corporation, the assignee herein. See also U.S. Pat. No. 4,201,891 entitled EXPANDABLE DIGITAL SWITCHING NETWORK assigned to the assignee herein and U.S. Pat. No. 4,201,889 entitled DISTRIBUTED CONTROL DIGITAL SWITCHING SYSTEM also assigned to the assignee herein.
In these systems a switching network architecture is provided wherein not only are multi-channel digitized PCM speech samples or data between one terminal and another carried by the network, but the same channels also contain the path selection and control signals for the distributed control, which are carried on the same transmission paths through the network. Every terminal, whether carrying data from a line or trunk or other data source, is serviced by a terminal unit which contains all the facilities and control logic to communicate with other terminals via other terminal units and to establish, maintain and terminate paths through the switching network to other terminal units. All interprocessor communication is routed through the switching network. A group switch containing switching elements providing both time and space switching is provided so that it is modularly expandable without disruption of existing connections.
In such a switching system as presently existing and as described in the above noted patents, it is recognized that there is a per channel band width which is limited as for example to 64 KB and that is not possible to establish multi-channel paths to increase the available bandwidth. This is true since the path setup mechanism does not provide for mutual frame integrity between paths between terminals on the same two clusters. Information samples which pass through different paths between the clusters experience different delays, effectively scrambling the output. This is a considerable problem in attempting to increase the bandwidth of such a distributed control switching system. Normal path setups in such a system are done as simplex, according to a hardware algorithm which minimizes real time delay along the path. As paths are setup through such a switch in the presence of other traffic; calls, data and messages on each path will be established with a different delay. Depending on such delays, the output word will be incorrectly delivered. As will be explained further, this will constitute a frame integrity problem which will cause the data as indicated above to be scrambled.
It is, therefore, an object of the present invention to provide apparatus which will enable the set up of multi-channel link paths to enable one to achieve a total bandwidth of N times 64 KB through such a switch. It is a further object to provide circuitry which will, in fact, establish and maintain integrity between such multi-path setups.